2,3-Dihydroperimidines as antioxidants for lubricants

ABSTRACT

Lubricants stabilized against oxidative degradation by the incorporation therein of 2,3-dihydroperimidine derivatives as well as certain 2,3-dihydroperimidines within the indicated group.

This invention relates to lubricant compositions which are stabilizedagainst oxidative decomposition by the addition of certain2,3-dihydroperimidine derivatives. More particularly, these compoundsare 2,3-dihydroperimidines substituted in the 2-position.

It is known to stabilize lubricants by the addition of antioxidantssuch, for example, as sterically hindered phenols, derivatives ofp-phenylene diamine or of diphenylamine in order to avoid decomposition,sludge formation, viscosity increases, and the like. U.S. Pat. No.3,535,243 also discloses the use of diaminonaphthalenes as antioxidativeadditives for ester lubricants. However, in mineral oils the solubilityof these additives is too low for practical use.

It has now been found that certain derivatives of 2,3-dihydroperimidineshow surprisingly high stabilizer activity and sufficient solubility ina wide variety of mineral and synthetic oils. Thus, the subject matterof the instant invention is a lubricant composition comprising a mineraloil, a synthetic oil or mixtures thereof and an antioxidative compoundcorresponding to formula I, ##STR1## wherein R¹ is hydrogen or alkylhaving 1 to 20 carbon atoms; R² is alkyl having 1 to 20 carbon atomswhich may be unsubstituted or substituted by a phosphono group orinterrupted by O or S, alkenyl having 3 to 16 carbon atoms, or arylhaving 6 to 10 carbon atoms which may be unsubstituted or substituted bylower alkyl, hydroxyl, halogen or di(lower)alkylamino, or

R¹ and R² together with the carbon atom to which they are attached arecycloalkane of 5 to 25 carbon atoms, alkylcycloalkane of 6 to 25 carbonatoms or cycloalkylcycloalkane of 9 to 25 carbon atoms; and

R³ and R⁴ are independently hydrogen or alkyl having 1 to 12 carbonatoms or R³ and R⁴ together are 1,2-ethylene in the peri-position.

R¹ and R² as alkyl may be straight- or branched-chain and may be, e.g.methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, n-pentyl, isoamyl,n-hexyl, 2-ethylbutyl, n-octyl, 2-ethylhexyl, isononyl, n-decyl,isoundecyl, n-dodecyl, 2,4-dimethylpentyl, 2,4,6-trimethylheptyl,n-hexadecyl, n-octadecyl or n-eicosyl. R¹ and R² as alkyl are preferablybranched-chain alkyl having 4 to 18 carbon atoms. R² may also be alkylinterrupted by O or S such, e.g, as 3-oxanonyl, 2-methyl-3-oxaheptyl,3-thiaheptyl or 2-methyl-3-thia-pentadecyl. R² may further be alkylsubstituted by a phosphono group, i.e. the group --P(O)(OR⁵)₂ wherein R⁵is lower alkyl or phenyl. Examples of such an R² group are, e.g.,2-diethylphosphono-ethyl, 2-methyl-2-dimethylphosphono-propyl or2-methyl-2-diphenylphosphono-propyl. R² as alkenyl includes, forexample, 1-propenyl, 10-dodecenyl or 2-pentyl-1-nonadecenyl.

R² as aryl or substituted aryl may be, e.g. phenyl, 4-chlorophenyl,4-tert.butylphenyl, 2-hydroxyphenyl, 4-dimethylaminophenyl, 1-naphthylor 2-hydroxy-1-naphthyl.

If R¹ and R² together with the carbon atom to which they are attachedform cycloalkane, alkyl- or cycloalkylcycloalkane groups, thecycloalkane group may be monocyclic or polycyclic. Examples of suchcyclic groups are cyclopentane, cyclohexane, mono- ordimethylcyclohexane, 4-tert.butylcyclohexane, 4-dodecylcylohexane, 2-,3- or 4-cyclohexyl cyclohexane, bicyclo[4.4.0]decane(decahydronaphthalene), tricyclo [5.2.1.0²,⁶ ]decane, cyclooctane orcyclododecane.

R³ and R⁴ as alkyl may be, e.g. methyl, ethyl, isopropyl, tert.butyl,n-hexyl, isooctyl or n-dodecyl. These alkyl groups may be attached inthe meta- or para-position to the nitrogen, i.e., in position 5, 6, 7 or8 of the perimidine ring system.

When R³ and R⁴ are 1,2-ethylene, this group is attached inperi-position, i.e. in position 6 and 7 of the perimidine ring system.

Within the given definition of lubricant stabilizers, there arepreferred classes. One preferred class includes compounds of formula Iwherein R¹ is hydrogen or branched-chain alkyl having 4 to 18 carbonatoms and R² is branched-chain alkyl having 4 to 18 carbon atoms.

Another preferred class includes compounds of the formula I wherein R¹and R² together with the carbon atom to which they are attached, form acycloalkane, alkylcycloalkane or cycloalkylcycloalkane group having 10to 20 carbon atoms.

A third preferred class includes compounds of formula I wherein R³ andR⁴ together form a 1,2-ethylene bridge in the peri-position.

Examples of compounds of formula I usable as antioxidative oil additivesinclude the following compounds:

2,2-diethyl-2,3-dihydroperimidine

2-methyl-2-isobutyl-2,3-dihydroperimidine

2-methyl-2-dodecyl-2,3-dihydroperimidine

2,2-dinonyl-2,3-dihydroperimidine

2-undecyl-2,3-dihydroperimidine

2-methyl-2-phenyl-2,3-dihydroperimidine

2-methyl-2-naphthyl-2,3-dihydroperimidine

2-heptyl-2-phenyl-2,3-dihydroperimidine

2,3-dihydroperimidine-2-spirocyclohexane

2,3-dihydroperimidine-2-spirocyclododecane

2,3-dihydroperimidine-2-spiro(decahydro-1-naphthalene)

2,2-dinonyl-2,3-dihydroaceperimidine

2-methyl-2-isoamyl-2,3-dihydroaceperimidine

2-heptyl-2,3-dihydroaceperimidine

2-methyl-2-phenyl-2,3-dihydroaceperimidine

2,3-dihydroaceperimidine-2-spiro(4-t-amylcyclohexane)

2,3-dihydroaceperimidine-2-spirododecane

2-(o-hydroxyphenyl)-2,3-dihydroaceperimidine

2,2-(N-methyl-3'-aza-pentaethylene)-2,3-dihydroperimidine

The lubricant may be an oil or a grease based on mineral or syntheticoils, these lubricants being well known to those skilled in the art. Theterm mineral oil includes all mineral oils used for lubricant purposes,such as hydrocarbon mineral oils. The synthetic oil may be, forinstance, an aliphatic or aromatic carboxylic ester, a polymeric ester,a polyalkylene oxide, a phosphoric acid ester, polyalphaolefins, or asilicone. Greases may be obtainable from these by adding metal soaps orsimilar thickeners.

The amount of compound of formula I added to the lubricant depends onthe sensitivity of the oil base to oxidation and on the desired degreeof protection. Generally, 0.01 to 2% by weight will be added, andpreferably 0.05 and 0.5%. The compounds of formula I may be used incombination with other antioxidants known as oil additives. Examplesthereof are aromatic amines, hindered phenols, aliphatic or aromaticphosphites, esters of thiodipropionic or thiodiacetic acid or salts ofdithiocarbamic or dithiophosphoric acids.

Such antioxidant combinations may show a synergistic action, i.e., thestabilizing effect of such a mixture being greater than the sum of theperformances of the individual antioxidants. Such synergisticperformance is obtained when combining compounds of formula I witharomatic amines or hindered phenols or with both types of antioxidants.

The lubricant composition may also contain other additives, such asmetal-passivating agents, rust inhibitors, viscosity regulators, pourpoint depressants, dispersing agents or detergents, said additives beingwidely known and used in lubricants.

The perimidine compounds of formula I can be prepared by known methodsof condensation of the corresponding 1,8-diaminonaphthalenes of formulaII ##STR2## wherein R³ and R⁴ are as previously defined, with ketones oraldehydes of the formula ##STR3## wherein R¹ and R² are as previouslydefined. The water formed in this reaction may be distilled off as anazeotropic mixture with toluene or xylene as is described in LiebigsAnnalen 365, 135 (1909). The reaction may be catalyzed by acids, such aspropionic acid, toluene sulfonic acid or trichloroacetic acid. Anothermethod of preparing these compounds proceeds by reduction of thecorresponding 1,8-dinitronaphthalenes in the presence of a carbonylcompound R¹ --CO--R², said process being described in GermanOffenlegungsschrift No. 2,155,544.

A number of the compounds falling within the scope of formula I havebeen disclosed in German Offenlegungsschrift No. 2,155,544 and inYamamoto et al, J. Am. Chem. Soc. 103, 4186-4194 (1981). Other compoundsare novel, however, and thus comprise part of the instant invention.These novel compounds correspond to the formula III ##STR4## wherein (1)R⁵ ═R¹, R⁶ ═R² and R⁵ R⁶ ═R¹ R² when R⁷ is hydrogen or alkyl having 1 to12 carbon atoms, R⁸ is alkyl having 1 to 12 carbon atoms, or R⁷ and R⁸together are 1,2-ethylene in the peri-position; or wherein (2) R⁵ and R⁶are branched-chain alkyl having 6 to 18 carbon atoms or R⁵ and R⁶together with the carbon atom to which they are attached formcycloalkane of 7 to 25 carbon atoms, alkylcycloalkane of 7 to 25 carbonatoms or cycloalkylcycloalkane of 9 to 25 carbon atoms, when R⁷ and R⁸independently are hydrogen or alkyl having 1 to 12 carbon atoms or R³and R⁴ together are 1,2-ethylene in the peri-position.

Compounds of interest within formula III include those wherein R⁵ and R⁶are branched-chain alkyl having 6 to 18 carbon atoms or R⁵ and R⁶together with the carbon atoms to which they are attached formalkylcycloalkane of 7 to 25 carbon atoms or cycloalkylcycloalkane of 10to 25 carbon atoms and R⁷ and R⁸ independently are hydrogen or alkylhaving 1 to 12 carbon atoms or R⁷ and R⁸ together are 1,2-ethylene inperi-position.

Other compounds of interest within formula III include those wherein R⁵and R⁶ together with the carbon atom to which they are attached form acycloalkane group having 5 to 20 carbon atoms, R⁷ is hydrogen or alkylhaving 1 to 12 carbon atoms and R⁸ is alkyl having 1 to 12 carbon atomsor R⁷ and R⁸ together are 1,2-ethylene in peri-position.

These new compounds are, of course, prepared in the manner describedhereinabove relative to the compounds of formula I.

The following examples will further illustrate the embodiments of theinstant invention.

EXAMPLE 1

A mixture of 15.8 g (0.1 mole) of 1,8-diaminonaphthalene and 16.8 g (0.1mole) of 4-t-amylcyclohexanone in 210 ml of toluene was heated underreflux. After the theoretical amount of water had been collected in aDean-Stark trap (3 hours), about 70 ml of toluene was distilled off. Theremaining solution was treated with 2.0 g of a filtration aid, filteredand the solvent removed in vacuo. Recrystallization from hexane gave28.45 g (92% yield) of2,3-dihydroperimidine-2-spiro(4-t-amylcyclohexane) as a tan solid, m.p.113°-115° C. (Compound No. 1)

C₂₁ H₂₈ N₂ (308.50): Calc.: C 81.77, H 9.15, N 9.08%. Found: C 81.69, H9.35, N 9.22%.

The following compounds were obtained in the same manner from1,8-diaminonaphthalene and the corresponding carbonyl compounds:

2,3-dihydroperimidine-2-spiro(4-t-butyl-cyclohexane), from4-t-butylcyclohexanone, light-brown solid, m.p. 168°-169° C. (CompoundNo. 2)

2,3-dihydroperimidine-2-spirocyclododecane, from cyclododecanone, graysolid, m.p. 195°-198° C. (Compound No. 3)

2,3-dihydroperimidine-2-spiro(decahydro-1-naphthalene), from1-oxodecahydronaphthalene, gray solid, m.p. 161°-162° C. (Compound No.4)

2,3-dihydroperimidine-2-spiro-8'tricyclo[5.2.1.0²,6 ]decane, from8-oxotricyclo[5.2.1.0²,6 ]decane, pink glassy solid, m.p. 50°-60° C.(Compound No. 5)

2,2-dinonyl-2,3-dihydroperimidine, from dinonyl ketone, gray solid, m.p.53°-54° C. (Compound No. 6)

2-methyl-2-(2-methyl-2-diethylphosphonopropyl)-2,3-dihyro perimidine,from 4-methyl-4-diethylphosphono-2-pentanone, pink solid, m.p. 102°-103°C. (Compound No. 7)

2-undecyl-2,3-dihydroperimidine, from dodecanal, pink solid m.p. 45°-50°C. (Compound No. 8)

2-(1-pentyl-1-octenyl)-2,3-dihydroperimidine, from 2-pentyl-2-nonenal,purified by column chromatography, pink oil (Compound No. 9)

C₂₄ H₃₄ N₂ (350.60): Calc.: C 82.23, H 9.78, N 7.99%. Formula: C 81.99,H 9.47, N 8.34%.

2-(3,5-di-t-butyl-4-hydroxyphenyl)-2,3-dihydroperimidine, from3,5-di-t-butyl-4-hydroxybenzaldehyde, recrystallized from toluene,colorless solid, m.p. 227°-228° C. (Compound No. 10)

2,3-dihydroperimidine-2-spiro(2-cyclohexylcyclohexane), from2-cyclohexyl-cyclohexanone, pink solid, crystallized from toluene as a1:2 toluene inclusion complex, m.p. 208°-210° C. (Compound No. 11)

2,3-dihydroperimidine-2-spiro(4-cyclohexylcyclohexane), from4-cyclohexyl-cyclohexane, tan solid, crystallized from toluene as a 1:2toluene inclusion complex, m.p. 152°-154° C. (Compound No. 12)

2,3-dihydroaceperimidine-2-spiro(4-t-amylcyclohexane), from5,6-diaminoacenaphthene and 4-t-amylcyclohexanone, tan solid, m.p.122°-129° C. (Compound No. 13).

2,3-dihydroaceperimidine-2-spirocyclododecane, from5,6-diaminoacenaphthene and cyclododecanone, tan solid, recrystallizedfrom toluene, m.p. 202°-203° C. (Compound No. 14)

2,3-dihydroperimidine-2-spirocyclohexane, from cyclohexanone, colorlesssolid, crystallized from ethanol- water (2:1), m.p. 108°-110° C.(Compound No. 15).

2,3-dihydroperimidine-2-spiro(4-t-octylcyclohexane), from4-t-octylcyclohexanone, pink glassy solid. (Compound No. 16).

EXAMPLE 2

15.8 g (0.1 mole) of 1,8-diaminonaphthalene and 16.0 g (0.1 mole) of2,5,7-trimethyl-4-nonanone were dissolved in a mixture of 52 g ofisobutanol, 24 g of water and 9 g of acetic acid and heated under refluxfor 11 hours. After cooling, the solution was neutralized with 3.0 g ofK₂ CO₃. The organic layer was separated from the aqueous layer andfiltered. The filtrate was evaporated in vacuo yielding a dark oilyresidue, which was thereafter dissolved in 2:1 hexane-diethylether andthe solution filtered over alumina. After distilling off the solvent,11.8 g of 2-isobutyl-2(2,4-dimethylpentyl)-2,3-dihydroperimidine wasobtained as a semi-solid residue (Compound No. 17)

C₂₂ H₃₂ N₂ (324.50): Calc.: C 81.43, H 9.94, N 8.63%. Found: C 81.02, H9.91, N 8.55%.

EXAMPLE 3

A solution of 3.2 g (0.02 mole) of 1,8-diaminonaphthalene and 3.0 g(0.02 mole) of p-dimethylaminobenzaldehyde in 35 ml of ethanol wasrefluxed for 2 hours. After cooling, the resulting precipitate wasfiltered and recrystallized from ethanol. There were obtained 3.8 g of2-(p-dimethylaminophenyl)-2,3-dihydroperimidine as colorless crystals,m.p. 165°-166° C. (Compound No. 18).

C₁₉ H₉ N₃ (289.37): Calc.: C 78.86, H.6.62, N 14.52%. Found: C 78.96, H6.64, N 14.45%.

EXAMPLE 4

The compounds of formula I were tested for their antioxidative effect inlubricants by the Rotary Bomb Oxidation Test (RBOT) according to ASTMD-2272.

In this test, 125 mg of the antioxidant and 5 ml of water are added to50 g of a mineral oil (Exxon LO-5084). Thus, the concentration of theantioxidant amounts to 0.25%. The lubricant is placed in a glasscontainer together with a copper coil. The glass container is placed ina steel bomb equipped with a pressure gage. The bomb is then chargedwith oxygen to a pressure of 90 psi (6.12 atm.), placed in an oil bathset at 150° C. and rotated axially at 100 rpm, at an angle of 30° fromthe horizontal. The test is completed after the pressure drops more than25 psi (1.7 atm).

The time in minutes from the start of the test to the 25 psi pressuredrop is reported in Table 1. As noted, the data show a significantimprovement in stability toward oxidation when the instant perimidinesare added to the oil.

                  TABLE 1                                                         ______________________________________                                        Compound No.                                                                            Time (min.)                                                                             Compound No.   Time (min.)                                ______________________________________                                        1         660        9             306                                        2         658       10             210                                        3         415       11             242                                        4         372       13             381                                        5         178       14             247                                        6         157       15             495                                        7         215       16             410                                        8         185       17             428                                                            18             381                                                            Control (without                                                              antioxidant)    30                                        ______________________________________                                    

EXAMPLE 5

Mixtures of compounds of formula I and commercial oil antioxidants weretested in the same manner as described in Example 4. As shown in Table2, these mixtures exhibit a synergistic activity.

                  TABLE 2                                                         ______________________________________                                        Additive                  RBOT (min.)                                         ______________________________________                                        0.25% Compound No. 3      415                                                 0.25% Irganox® L 57   146                                                 0.25 Irganox® L 130   114                                                 0.25% Irganox® L 01   120                                                 0.05% No. 3 + 0.20% Irganox® L 57                                                                   315                                                 0.05% No. 3 + 0.20% Irganox® L 130                                                                  315                                                 0.05% No. 3 + 0.10% Irganox® L 57 +                                       0.10% Irganox® L 130  434                                                 0.05% No. 3 + 0.20% Irganox® L 01                                                                   276                                                 0.25% Compound No. 1      660                                                 0.05% No. 1 + 0.20% Irganox® L 57                                                                   382                                                 0.05% No. 1 + 0.10% Irganox® L 57 + 0.10%                                 Irganox® L 130        377                                                 0.05% No. 1 + 0.20% Irganox® L 01                                                                   303                                                 0.25% Compound No. 11     306                                                 0.05% No. 11 + 0.20% Irganox® L 130                                                                 232                                                 0.05% No. 11 + 0.20% Irganox® L 115                                                                 230                                                 0.25 Compound No. 17      428                                                 0.05% No. 17 + 0.20% Irganox® L 01                                                                  229                                                 ______________________________________                                         Legend:                                                                       Irganox® L57 = dialkyl diphenylamine                                      Irganox® L130 = liquid phenolic antioxidant                               Irganox® L01 = 4,4dioctyldiphenylamine                                    Irganox® L115 =                                                           thiodiethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamate).                   Irganox products from CIBAGEIGY Corp.                                    

In summary, this invention provides a novel class of lubricantantioxidants which exhibit excellent antioxidative performance.Variations may be made in procedures, proportions and materials withoutdeparting from the scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A lubricant composition comprising a mineral oilor a synthetic oil or mixtures thereof and an effective stabilizingamount of a compound of formula (I) ##STR5## wherein R¹ is hydrogen oralkyl having 1 to 20 carbon atoms; R² is alkyl, phosphono-substitutedalkyl, alkyl interrupted by O, alkyl interrupted by S, alkenyl having 3to 16 carbon atoms, aryl, lower alkyl-substituted aryl,hydroxyl-substituted aryl, halogen-substituted aryl or di(lower)alkylamino-substituted aryl and wherein said alkyl group has from 1 to20 carbon atoms and said aryl group has from 6 to 10 carbon atoms or R¹and R² together with the carbon atom to which they are attached formcycloalkane of 5 to 25 carbon atoms, alkylcycloalkane of 6 to 25 carbonatoms or cycloalkylcycloalkane of 9 to 25 carbon atoms; and R³ and R⁴independently are hydrogen or alkyl having 1 to 12 carbon atoms or R³and R⁴ together are 1,2-ethylene in the peri-position.
 2. A lubricantcomposition according to claim 1 containing a compound of formula Iwherein R¹ is hydrogen or branched-chain alkyl having 4 to 18 carbonatoms and R² is branched-chain alkyl having 4 to 18 carbon atoms.
 3. Alubricant composition according to claim 1 containing a compound offormula I wherein R¹ and R² together with the carbon atom to which theyare attached form a cycloalkane, alkylcycloalkane orcycloalkylcycloalkane group having 10 to 20 carbon atoms.
 4. A lubricantcomposition according to claim 1 containing a compound of formula Iwherein R³ and R⁴ together form a 1,2-ethylene bridge in theperi-position.
 5. A lubricant composition according to claim 1, whereinsaid compound is selected from the group consisting of2,3-dihydroperimidine-2-spiro(4-t-amyl-cyclohexane),2,3-dihydropermidine-2-spiro(4-t-butyl-cyclohexane),2,3-dihydroperimidine-2-spirocyclododecane,2,3-dihydroperimidine-2-spiro(decahydro-1-naphthalene),2,3-dihydroperimidine-2-spiro-8'-tricyclo[5.2.1.0²,6 ]decane,2,2-dinonyl-2,3-dihydroperimidine,2-methyl-2-(2-methyl-2-diethylphosphonopropyl)-2,3-dihydroperimidine,2-undecyl-2,3-dihydroperimidine,2-(1-pentyl-1-octenyl)-2,3-dihydroperimidine,2-(3,5-di-t-butyl-4-hydroxyphenyl)-2,3-dihydroperimidine,2,3-dihydroperimidine-2-spiro(2-cyclohexylcyclohexane),2,3-dihydroperimidine-2-spiro(4-cyclohexylcyclohexane),2,3-dihydroaceperimidine-2-spiro(4-t-amylcyclohexane),2,3-dihydroaceperimidine-2-spirocyclododecane,2,3-dihydroperimidine-2-spirocyclohexane,2,3-dihydropermidine-2-spiro(4-t-octylcyclohexane),2-isobutyl-2-(2,4-dimethylphenyl)-2,3-dihydroperimidine and2-(p-dimethylaminophenyl)-2,3-dihydroperimidine.